1. Field of the Invention
The present invention relates to a method of manufacturing an oxide high-temperature superconductor thin film by means of a molecular-beam epitaxy (to be referred to as an MBE hereinafter).
2. Description of the Related Art
Conventionally, various film formation methods including a magnetron sputtering method, a laser sputtering method, a reactive vapor deposition method, and an MBE method have been attempted in the manufacture of an oxide high-temperature superconductor thin film.
In any of these methods, a structure of an oxide superconductor can be formed by precisely controlling film formation conditions.
In addition, various types of oxidation gases are used to incorporate oxygen into crystals, and it is known that a temperature required for formation of an oxide film changes in accordance with the type of gas used.
For example, in crystallization of a Bi--Sr--Cu--O superconductor, the crystallization conditions are as follows:
Oxidation temperature: 500.degree. C. or more Required vacuum degree corresponding to type of oxidizing agent PA0 oxygen gas (O.sub.2) 10.sup.-2 to 10.sup.-3 Torr PA0 ozone (O.sub.3) : 10.sup.-5 Torr
As described above, even when ozone which is conventionally considered to be most active is used, the crystallization temperature must be 500.degree. C. or more, and generally, 600.degree. C. to 700.degree. C.
In addition, even when a highly active gas such as ozone is used, a required vacuum degree is at most about 10.sup.-5 Torr, i.e., outside a high vacuum range.
However, when an application of an oxide superconductor is taken into consideration, in particular, to form a composite structure with various types of other materials as electronics devices, a temperature of 500.degree. C. is too high and therefore impractical in terms of the heat resistances of the electronics devices.
Furthermore, to obtain a high-quality thin film by the film formation methods as described above, it is desired to execute film formation at a pressure as low as possible, i.e., within a high vacuum range. However, even when ozone having the highest activity is used, a gas pressure upon film formation must be 10.sup.-4 to 10.sup.-5 Torr or more. This pressure value is far from an ideal low pressure value for obtaining a high-quality thin film.